1. Technical Field
The present invention relates to a separation technique for separating pieces made of a specific material from a group of pieces that is a separation subject and, more particularly, the present invention relates to a separation technique for separating pieces made of a specific class of resins from a separation subject obtained by crushing used home appliances.
2. Description of the Related Art
Economic activities in recent years represented by mass production, mass consumption, and mass disposal have been causing global environmental problems such as global warming and depletion of resources. Under such circumstance, attention has been paid to the recycling of home appliances, and recycling of used home appliances such as air conditioners, televisions, refrigerators/freezers, and washing machines has become mandatory, in an effort to build a recycling society.
Conventionally, unneeded home appliances have been recycled by crushing them into small pieces in home appliance-recycling plants and separating the small pieces by material, using magnetism, wind, oscillation, etc. In particular, the use of a specific-gravity separation apparatus or a magnetism separation apparatus allows small pieces made of metal to be separated by metal species such as iron, copper, and aluminum in very pure form. This achieves a high recycling rate.
On the other hand, as to resin materials, small pieces made of polypropylene (hereinafter referred to as PP) that has a low specific gravity are separated from a component having a high specific gravity through specific separation using water, and thus are recovered with a relatively high degree of purity. This specific gravity separation using water, however, has major problems that; an enormous amount of wastewater is produced and that; small pieces made of polystyrene (hereinafter denoted as PS) and small pieces made of acrylonitrile-butadiene-styrene (hereinafter denoted as ABS), which have similar specific gravities, are not separated from each other.
Japanese Unexamined Patent Application Publication No. 2002-263587 suggests a separation method in view of the above problem related to recycling of resin materials.
The technique disclosed by JP 2002-263587 uses a material distinguishing unit to detect a material, thereby enabling separation of resin materials which are inseparable by specific gravity separation.
To be specific, materials of separation subjects conveyed on a conveyor belt are distinguished for each group of small pieces with the material distinguishing unit, and in order to separate the distinguished resin items made of a specific resin material from the trajectories of the separation subjects thrown forward from a conveying end of the conveyor belt. In the separation method, pulse air is discharged from nozzles provided above or below the trajectories of the separation subjects so as to blow off small pieces of a specific material and separate from a group of the separation subjects.
The conventional method for separating separation subjects that is recited in JP 2002-263587 will be further described in detail with reference to drawings.
FIGS. 7a to 7c and 8 illustrate an example of a conventional method for separating separation subjects. FIGS. 7a to 7c are side views of a process for separating pieces 2A made of any specific material from small pieces 2A, 2B, 2C, and 2D conveyed by a conveyor 1. FIG. 8 is a plan view of the process.
FIG. 7a illustrates small pieces 2A, 2B, 2C and 2D as separation subjects conveyed by the conveyor 1, and the small pieces 2A is made of any specific material. The numerical reference 3 in FIG. 7a indicates a material distinguishing unit. The numerical reference 4 in FIG. 7a indicates a conveying end of the conveyor 1, from which the small pieces 2A, 2B, 2C, and 2D are thrown forward. The numerical reference 5 in FIG. 7a indicates a nozzle group provided in the width direction of the conveyor 1 to separate the small pieces 2A of a specific material from the trajectories of the small pieces 2A, 2B, 2C, and 2D that have been thrown forward from the conveying end 4. The numerical reference 8 in FIG. 7A indicates a separation plate for separating the small pieces 2A of the specific material that has been separated from the trajectories of the small pieces 2A, 2B, 2C, and 2D. It should be noted that FIG. 7a is a side view and FIG. 8 is a plan view of the same scene as the scene shown in FIG. 7a. 
FIG. 7b illustrates that the material distinguishing unit 3 distinguishes the materials and shapes of the separation subjects 2A, 2B, 2C, and 2D when the separation subjects are passing under the material distinguishing unit 3.
FIG. 7c illustrates that the small pieces 2A, 2B, 2C, and 2D distinguished by the material distinguishing unit 3 are thrown forward from the conveying end 4. Moreover, when the small pieces 2A of any specific material pass under a group of nozzles 5, pulse air is discharged only from a nozzle of the group of nozzles 5, corresponding to the small pieces 2A so as to blow off the small pieces 2A of any specific material and separate from the small pieces of other materials. Moreover, representative trajectories of the small pieces 2A, 2B, 2C, and 2D thrown forward from the conveying end 4 of the conveyor 1 are represented by a solid line, a broken line, and a dashed-dotted line.
Thus, according to the conventional separation method recited in JP 2002-263587, a material distinguishing unit and pulse air can separate items made of a specific material from a group of the separation subjects. Therefore, it is possible to separate PS and ABS which have similar specific gravities.
It should be noted that in the conventional separation method recited in JP 2002-263587, since one specific material is separated by separation processing at one time, separation processing is performed several times to separate two or more specific materials from a group of the separation subjects.